I just heard Elon say that the Model S will feature a 90 kWh battery (300 mile version i presume) and that the gravimetric energy density has incresed about 30-35%.
I also heard him say that the cells in the Model S uses a quarter the amount of cobalt compared with the roadster cells.
Based on this, and the roadster specs, the weight of the Model S battery will be about 535-556 kg, and the chemistry used in the cells is probably NCA (LiNiCoAl02 cathode and graphite anode).
Panasonic has NCA cells scheduled to begin production in 2012
The cycle life of these cells seem the be very good if you cycle them between 4.1 and 3.0 Volts (80% capacity after 5000+ cycles)
So what i am trying to get at is what voltage range the cells will be kept in and how many cells the battery consists of.
If kept between 4.1 and 3.0 Volts the cells capacity will be about 85% of the rated capacity.
A 90 kWh battery built with Panasonic 3.4 Ah 18650 cells will then require about 8650 cells.
If you would use the rated capacity, 12.24 Wh per cell, then the number of cells required would be about 7350.
If you assume the ratio between cell mass, and total battery pack mass is the same as the roadster, about 0.66, then the number of cells would be 7820 (using 545 kg as total weight).
That gives a 11.5 Wh capacity per cell, or 94% of rated capacity.
So that do you think? are my assumptions right about the NCA chemistry? how many cells does it use? do you think they have improved (incresed) the total cell mass/battery mass ratio? what voltage range will the cells be kept between?